Wireless networks include, amongst other things, access points and user devices. User devices can be any device with an interface capable of enabling wireless networking using a wireless network, including, for example, laptops. Access points are devices which enable a user device to access a particular wireless network using, for example, Bluetooth or Wi-Fi. Once a user device has access to a wireless network it can send and receive data over the network.
It can be useful to estimate a user's location within a wireless network, for example if the services provided to a user device are dependent upon the location of the user device within the network. This is of particular difficulty when the user devices are mobile and therefore the components in the network are not static in nature.
In order to determine the location of devices within networks that can be accessed by mobile devices several solutions have been proposed. These include RF fingerprinting, time of arrival trilateration and use of a GPS device on the mobile device.
RF fingerprinting involves a survey of the area covered by the wireless network and evaluating the RF spectrum at certain points within the area. The system, or the mobile unit itself, can determine the RF spectrum of the user device and compare it to the RF spectrum of different points in the area as measured from the survey. This comparison can be used to define where the user device is in the network. However, this method of location determination requires resources to determine the received RF spectrum of points within the area. Furthermore, dynamics within the RF environment of the area can change, increasing the error in location estimation.
Time of arrival trilateration involves access points determining the time of flight for a transmission from a user device to the access point. From this time of flight a distance from the access point can be determined and the meeting point of these distances is an estimate of the location of the user device. However, to accurately estimate location using time of arrival trilateration requires a user device to be able to communicate with at least three access points within the network which may mean that the number of access points required to estimate location is greater than that required to service the network. Additionally, the estimation of time must be accurate with differences between the clocks on the user device and those on the access points resulting in time, and hence location, estimation errors.
Finally, the use of a GPS receiver, or other location determination equipment, in the user device can be used to determine the location of the user device. However, this is dependent upon the visibility of satellites at the point where the user device is located which may not be possible within a building. Providing each user device with a GPS receiver can also be costly.
Therefore, it is desirable to have an improved way of estimating the location of a user device in a wireless network.